1/22/2024 0 Comments Far field diffraction definitionMoreover, the peak intensity of the sagittal focus is maximum, and the ratio of the peak intensity to that in the meridian plane is approximately 1.5. But the locus of the sagittal foci is obviously different from the locus of the meridian foci and the catacaustic focus. In addition, we find that the difference in locus between the catacaustic and the diffraction focus in the meridian is small. The variation in the Strehl ratio with oblique incidence angle strongly depends on the misalignment direction and beam size as well. The incident polarization also affects the intensity distribution. Coma-like aberration starts to become dominant with beam size increasing and results in larger curved propagation trajectory. The intensity distribution produces a higher astigmatic image with off-axis angle increasing. The focal shift strongly depends on the effective focal length and oblique incidence angle, but it is almost independent of the beam size, which affects the focusing spot patterns. The radius of 90% encircled energy also increases but does not change monotonically with incident beam size increasing, or rather, it first decreases and then increases. The results show that the far-field intensity profile is altered by the distortion-, coma-, and astigmatism-like aberrations, which are caused by oblique incidence rather than inherent aberrations for the off-axis configuration. The physical origin of these effects is also explored. Based on a full vector-diffraction theory, a detailed theoretical study is carried out, aiming at providing a clear insight into the effects of different focusing and off-axis parabola parameters on far-field vector-diffraction properties of an off-axis parabolic mirror in the presence of misalignments of the incoming beam.
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